[Brian]

Sorry for the trouble, eemala!

If you select the tasks in question, then open the Schedule tab of the Tasks inspector, are the start and/or end dates on those tasks locked?

In other words, are the small padlock icons above those fields "closed" or "open"? Are you able to click into those fields and enter new dates from the keyboard?

If the start/due dates are locked, that could cause the same symptoms you're describing. Does that help at all?